1. Field of the Invention
This invention relates to welding apparatus and especially to such apparatus designed for resurfacing the interior of pipe having a relatively small diameter.
2. Description of the Prior Art
In many fields of endeavor, it is desirable to rebuild old structural components in lieu of the purchase of expensive new components. In the oil business especially, it is desirable to repair deteriorated items such as the stuffing boxes used in well drilling rigs and well pumps, as the major structural integrity of these elements is maintained and only the inner peripheral surface becomes worn and unusable. The present procedure for effecting such repairs calls for a manual welding operation in which the welder must toil for some nine hours in order to insure that the entire peripheral surface of the stuffing box is rebuilt with a quality weld. There has, therefore, developed a demand for a welding apparatus which will perform this function quickly, effectively and economically.
However, due to the nature of the structure to be welded, stuffing boxes normally have a length of approximately 14 inches with an internal diameter of approximately 4 inches, conventional welding machines and techniques are inappropriate in that they either are too cumbersome to fit within the confines of the stuffing box or are so complex as to destroy the economic benefit derived from resurfacing of the stuffing boxes. Among the prior art welding machines, are included certain machines designed to weld internally of the hollow structures. Examples of such machines include U.S. Pat. No. 3,009,048, issued Nov. 14, 1961 to Stanley, and U.S. Pat. No. 3,817,400, issued June 18, 1974 to Bartley. Each of these patents discloses a welding machine which is disposed in its entirety within the confines of a hollow structure to be welded. The welding machine is movable axially within the structure and the welding head is rotatable through an arc along the inner periphery of the structure. A machine such as this is not amenable to use within the confines of small pipes or stuffing boxes. Each of U.S. Pat. Nos. 4,068,791, issued Jan. 17, 1978 to Scholtus et al, and 3,769,486, issued Oct. 30, 1973 to Braucht shows a welding apparatus in which the head of a welding machine is insertable within a hollow structure. The head is disposed for movement axially within the structure as well as attached for rotation about the circumference of the internal surface of the structure. Devices such as these require complex mechanical linkages in order to insure the proper totality of movement of the welding head necessary to effect a smooth, clean weld. Also, due to the complexity of the head movement linkages, it is customary to utilize a sensing device in order to maintain a proper distance between the welding electrode and the surface being welded. The devices disclosed in U.S. Pat. Nos. 3,084,243, issued Apr. 2, 1963 to Gotch, 3,020,388, issued Feb. 6, 1962 to Elliott, 3,582,599, issued June 1, 1971 to Yohn, and 3,437,787, issued Apr. 8, 1969 to Chyle are welding devices designed to produce a single bead axially of a pipe in the pipe wall. Thus, none of these devices would be suitable for producing a continuous deposit of weld material on the internal surface of a pipe. In like manner, the devices disclosed in U.S. Pat. No. 3,424,877, issued June 28, 1969 to Fehlman, and U.S. Pat. No. 1,846,470, issued Feb. 23, 1932 to Burnish will be unable to deposit a layer of weld material on the internal surface of a pipe as each of these patents discloses a welding device designed to produce a single circular weld on the inner periphery of a pipe and no axial movement of the weld head is contemplated.